Guitar Chords - Playing Piano for Singing
As you are playing piano for singing (I call this ChordPlay), this works really well using guitar chords eg using Ultimate Guitar, as you don't need to play the melody. The instruction as to which chord to play doesn't change between guitar and piano, the difference is the playing patterns that you use to play the chords.
An easy beginners way is to play the 'root' chord in the right hand (I call it the 'claw' shape eg notes c e g for for C and f a c for chord F etc... and the chord note in the left hand eg note c for chord C note f for chord F etc.. The left hand often doubles up these notes (same note but played in 2 octaves).
More advanced patterns then add rhythms, arpeggios and inversions to change the order of these same notes and then 'expert' levels include adding passing notes, riffs and improvisation / creating more complex chord variants.
The UG chord charts on each chord sheet show you the 'claw' shape for each chord and a 1 minute quick guide is below:- and free tutorials on using UG chords to play Hallelujah and Perfect are at www.DecPlay.com
Using Guitar Chords to Learn Solo Piano
If you are playing solo piano eg where you are playing instrumental music and need to play the melody, then the beginners method is to play the chord in the left hand and the melody in the right hand (FastPlay).
The advanced way to play this is adding the melody to the ChordPlay method mentioned above, with the right hand playing both the chords and the melody (ProPlay).
The easiest way to play the melody is using piano tabs like PianoTabz.com which is much easier than notation. This enables beginners to understand the written music within minutes and enables the full range of playing styles from beginners to advanced.